Mendel and Mendelian Genetics I Gregor Mendel Heredity

Mendel and Mendelian Genetics

I. Gregor Mendel • Heredity – passing of characteristics (traits) from parents to offspring • Genetics – biology that studies heredity

II. Pea Plant Experiments • Breeding pea plants – Reproduce sexually • Fertilization – gametes form zygote (fertilized cell) • Pollination – pollen grains from male to female

II. Pea Plant Experiments • Cross pollination – breed one plant with another (did it manually)

II. Pea Plant Experiments • Mendel observed seven characteristics. • Each occurred in two contrasting traits.

II. Pea Plant Experiments (Monohybrid Cross) • Mendel crossed short plant with tall plant (P Generation). • ALL offspring (hybrids) were tall. (F 1 Generation) • 2 nd Generation (F 2) – tall plants from 1 st generation to self-pollinate

III. Mendel’s Conclusions • Each organism has two factors that control each trait • Alleles – genes in alternative form • Genes – parts of chromosomes (DNA) that control specific characteristics

III. Mendel’s Conclusions • Organisms ALWAYS have two alleles (one on each chromosome) • Alleles can be either dominant or recessive

III. Mendel’s Conclusions • Dominant trait – masks the presence of other traits for the same characteristic • Recessive trait – is masked by dominant trait for the same characteristic

IV. Rule of Dominance • If an organism had one dominant allele, this trait would be expressed, hiding the recessive trait • Capital letters = Dominant allele • Lowercase = Recessive

V. Law of Segregation 1) There alternate versions of genes called alleles. 2) For each characteristic, an organism inherits two alleles. 3) Alleles interact in a number of ways. 4) The two alleles for a trait separate during gamete production

Vocabulary • Phenotype – observed characteristics (example: long or short neck) • Genotype – genetic makeup of an individual (example: Nn or nn)

Vocabulary • Homozygous – two of the same alleles • Homozygous dominant two dominant alleles (TT) • Homozygous recessive – two recessive alleles (tt)

Vocabulary • Heterozygous – two different alleles (Tt) • One is dominant and one is recessive

Example • Long necks in giraffes are dominant to short necks (N and n) • Genes vs. displayed trait

VII. Law of Independent Assortment • Inheritance of one trait will not affect the inheritance of another. • Only true for traits not linked.

VIII. Punnett Squares • Reginald Punnet (1905) developed Punnet squares. Monohybrid Cross

VIII. Punnett Squares • Shows probability, yet not exact outcomes (genetics follows rule of chance)